The present invention relates generally to antenna arrays, and more particularly, to an inverted boxhorn antenna array.
One conventional antenna array is known as a boxhorn array, which is a particular arrangement of boxhorn antenna elements placed in rectangular arrays or in echelon arrays that are fed from a true-time-delay waveguide corporate power divider. The boxhorn antenna elements may be flared in the E-plane. Dielectric loading may be employed to reduce the size of the boxhorn array. The boxhorn array may also be formed using a plurality of arrays. Although normally uniformly excited, tapered amplitude and phase designs may be made. The main beam generated by the boxhorn array is normal to the face of the array at all frequencies, and thus the array has no beam squint. Boxhorn elements were first developed during World War II and their design parameters were reported in a book by S. Silver entitled "Microwave Antenna Theory and Design" published by McGraw-Hill, 1949, pp. 377-380.
Boxhorn arrays are linearly polarized along one of the principal axes of the array. For low sidelobe line-of-sight microwave communications applications, such arrays are typically equipped with 45-degree transmission-type twist polarizers. These polarizers rotate the plane of polarization into a diagonal plane. When the array is mounted with the diagonal oriented horizontally, the horizontal plane sidelobes are greatly improved and the resulting antenna complies with demanding international specifications for horizontal plane sidelobes. Frequency ranges of such boxhorn arrays are typically 2-40 GHz. Bandwidths up to 12 percent can be accommodated.
Typically, the boxhorn array includes two metal components, a one-piece array face containing the boxhorn antenna elements and a one-piece power divider. In this case, the two components are fastened together with screws. This is known as and is referred to herein as a standard boxhorn array. However, in certain applications, it would be desirable to further reduce the size of the boxhorn array.
Furthermore, the heart of the boxhorn array is the power divider (or combiner). In typical boxhorn arrays having gains in the 35-43 dBi range, power dividers from 512-way to 4,096-way are required. Design and fabrication of such dividers presents great difficulties in performance, fabrication tolerances and production costs of conventional boxhorn arrays. It would be advantageous to have a boxhorn antenna structure that minimizes the complexity of the power dividers used therein.
Accordingly, it is an objective of the present invention to provide for an inverted boxhorn antenna array that overcomes limitations found in conventional boxhorn arrays. It is another objective of the present invention to provide for an inverted boxhorn antenna array that has reduced size compared to the standard boxhorn array. It is yet another objective of the present invention to provide for an inverted boxhorn antenna array that minimizes the complexity of the power dividers used therein.